Enable libsdl2 component

Currently, libsdl2 is not included in the target image basically.
Because nothing requires the component, but it may be used somewhere
in the future.

To support it, add libsdl2 into packagegroup to install by default.

Fix: webosce/README#9

Signed-off-by: Yi-Soo An <yisooan@gmail.com>

meta-webos/recipes-core/packagegroups/packagegroup-webos-extended.bb

@@ -99,6 +99,7 @@ RDEPENDS_${PN} = " \
     sam \
     settingsservice \
     sleepd \
+    libsdl2 \
     webos-connman-adapter \
     webos-fontconfig-files \
     ${VIRTUAL-RUNTIME_appinstalld} \